Bacterial Lipoprotein Delays Apoptosis in Human Neutrophils through Inhibition of Caspase-3 Activity: Regulatory Roles for CD14 and TLR-2

Department of Academic Surgery, National University of Ireland, Cork University Hospital.
The Journal of Immunology (Impact Factor: 4.92). 11/2004; 173(8):5229-37. DOI: 10.4049/jimmunol.180.1.664
Source: PubMed


The human sepsis syndrome resulting from bacterial infection continues to account for a significant proportion of hospital mortality. Neutralizing strategies aimed at individual bacterial wall products (such as LPS) have enjoyed limited success in this arena. Bacterial lipoprotein (BLP) is a major constituent of the wall of diverse bacterial forms and profoundly influences cellular function in vivo and in vitro, and has been implicated in the etiology of human sepsis. Delayed polymorphonuclear cell (PMN) apoptosis is a characteristic feature of human sepsis arising from Gram-negative or Gram-positive bacterial infection. Bacterial wall product ligation and subsequent receptor-mediated events upstream of caspase inhibition in neutrophils remain incompletely understood. BLP has been shown to exert its cellular effects primarily through TLR-2, and it is now widely accepted that lateral associations with the TLRs represent the means by which CD14 communicates intracellular messages. In this study, we demonstrate that BLP inhibits neutrophil mitochondrial membrane depolarization with a subsequent reduction in caspase-3 processing, ultimately leading to a significant delay in PMN apoptosis. Pretreatment of PMNs with an anti-TLR-2 mAb or anti-CD14 mAb prevented BLP from delaying PMN apoptosis to such a marked degree. Combination blockade using both mAbs completely prevented the effects of BLP (in 1 and 10 ng/ml concentrations) on PMN apoptosis. At higher concentrations of BLP, the antiapoptotic effects were observed, but were not as pronounced. Our findings therefore provide the first evidence of a crucial role for both CD14 and TLR-2 in delayed PMN apoptosis arising from bacterial infection.

Download full-text


Available from: Noel Aherne
  • Source
    • "Its function in these cells is even more obscure. The membrane bound form of CD14 has been related to apoptosis in different ways; it was suggested to act as a tethering receptor for apoptotic cells on the surface of phagocytes, to facilitate removal of apoptotic cells, and also as a surface membrane molecule possibly associated with resistance from apoptosis of monocytes, neutrophils and, as demonstrated recently, of enterocytes, challenged with LPS (Gregory 2000; Devitt et al. 1998; Heidenreich et al. 1997; Heidenreich 1999; Yu et al. 2006; Devitt et al. 2004; Power et al. 2004). Whether soluble CD14 has additional functions or activities related to apoptosis is less established. "
    [Show abstract] [Hide abstract]
    ABSTRACT: CD14 is a 56 Kd glycoprotein typically present on myeloid cells and originally implicated in innate immunity and pattern recognition. The possible involvement of its membrane bound form with the clearance of apoptotic cells and its recently demonstrated expression by non-myeloid cells, make this fascinating molecule a target for more research and possible therapeutic use. The objective of this study was to assess the possible anti apoptotic effect of the soluble form of CD14, on human lymphocytes and to delineate the fragment, from within the protein that may be mediating that activity. Human peripheral blood lymphocytes were cultured in vitro and induced for apoptosis with gliotoxin, with or without the addition of rhCD14 or CD14 peptide. As controls, we used lymphocyte cell lines such as Jurkat, NK-YTS and also normal peripheral blood neutrophils. We demonstrate that human soluble CD14 is capable of protecting human lymphocytes from gliotoxin- induced apoptosis in vitro. It is not capable of protecting gliotoxin-treated apoptotic Jurkat or NK-YTS cells. Moreover, we reveal that a fragment of the protein, a peptide that is recognized by the MO2 monoclonal anti-CD14 antibody, retains this protective effect, although with a lower efficiency. We have previously shown that the MO2 epitope was found naturally inside human lymphocytes. Here, we demonstrate that the MO2 peptide can penetrate lymphocytes in human peripheral blood mononuclear cells incubated in vitro. The peptide does not penetrate Jurkat or NK-YTS cells and it does not protect them from apoptosis. In addition, peripheral blood neutrophils, in which the peptide penetration was much better than in lymphocytes, could not be protected by this peptide from their spontaneous apoptosis in vitro.Our data thus suggest that circulating CD14 may play an important role in the prevention of apoptosis of lymphocytes and that a specific region from within the molecule is involved in this activity.
    Full-text · Article · Sep 2012 · International Journal of Peptide Research and Therapeutics
  • Source
    • "Sohn et al. (2007) have reported that bovine CD14 + PMN bound to LPS resulted in a downregulation of apoptosis. Moreover, CD14 expression delayed PMN apoptosis triggered by bacterial lipoproteins and lipoteichoic acid (Lotz et al., 2004; Power et al., 2004). "
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper investigates the association between expression of CD14 and occurrence of apoptosis in blood, resident ((RES)PMN) and inflammatory ((INF)PMN) polymorphonuclear leukocytes (PMN) from heifer mammary glands. The fresh population of (RES)PMN contained a statistically significant higher proportion of CD14+, apoptotic and necrotic cells than did populations of (INF)PMN and blood PMN. In vitro cultivation of (RES)PMN, (INF)PMN and blood PMN led to concurrent increase of apoptotic, necrotic and CD14+ cells. A positive correlation was found between the proportions of both apoptotic and necrotic PMN and CD14+ PMN as determined by three-color flow cytometry analysis. Our study confirmed that expression of CD14 in blood PMN, (RES)PMN and (INF)PMN from heifer mammary glands was accompanied by apoptosis and necrosis.
    Full-text · Article · Apr 2011 · Research in Veterinary Science
  • Source
    • "Neutrophil accumulation at the inflammatory foci and survival have been implicated in the pathology of other inflammatory diseases such as arthritis, meningitis and peritonitis [27] [29]. As previously observed for other bacterial lipoproteins [16], B. abortus lipoproteins mediated apoptotic delay. Hence, by delaying apoptosis B. abortus lipoproteins may further contribute to the pathogenesis of brucellosis, over-riding apoptotic neutrophils removal by phagocytic cells and limiting inflammation resolution. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Human brucellosis is caused by infection with certain species of the genus Brucella and is characterized by bacterial persistence and inflammation of many host tissues. Neutrophils are one of the predominant cell types present in the infiltrate of these inflamed tissues, and due to their potential effect on the inflammatory response and tissue damage, direct activation of neutrophils by Brucella abortus might contribute to the pathology associated with human brucellosis. B. abortus expresses outer membrane lipoproteins (Omp) with inflammatory properties on a variety of cell types. This study examines the effect of B. abortus and its lipoproteins on neutrophil functions. B. abortus induced an increment in CD35 and CD11b expression and a decline in CD62L accompanied by IL-8 secretion, a response compatible with neutrophil activation. B. abortus lipoprotein Omp19 (L-Omp19), but not its unlipidated form, mimicked the changes associated with neutrophil activation induced by B. abortus. L-Omp19 primed neutrophils for oxidative burst as well as promoted neutrophil migration and prolonged neutrophil survival. Thus, Brucella lipoproteins possess pro-inflammatory properties that could contribute to the localize tissue injury and inflammation by direct activation of neutrophils. Data presented here, together with our previous results implicate Brucella lipoproteins in the pathogenesis of human brucellosis.
    Full-text · Article · May 2009 · Microbes and Infection
Show more